1. Field of the Invention
The present invention relates to the recovery of data from a damaged recording medium or a recording medium with a writing error.
2. Brief Description of Prior Developments
Previously, conventional or traditional data recovery techniques have required that a synchronization mark be readable. Errors in synchronization marks have traditionally been minimized during the format of a recording medium by providing a flag before bad or unreadable sectors of a disk. In this fashion, a disk drive controller is able to skip any sector likely to yield errors in data reading and writing.
For situations when a synchronization mark becomes damaged or unreadable after format of the recording medium, alternate techniques have been developed. For example, fault tolerance techniques can be used to read marks which have not been destroyed beyond recognition. With these techniques, the correction capability is encoded into the mark itself. For example, a mark can be encoded with numerous bits, which can be sub-divided into different regions. One method allows for a certain number of these regions to be in error i.e., unreadable. A controller instructs the system to continue as if no error in reading the mark occurred within a pre-defined error tolerance. Another method that has been used is the encoding of synchronization marks with redundant or duplicate data, so that if one portion of the mark is unreadable, the head can still read a copy of the information.
Another previous fault tolerance technique involves the movement of the recording/reading head to one side or another by a predefined per cent. For example, if a synchronization mark is determined to be unreadable, the head can be moved offtrack by 10%. If the mark is still unreadable, the head can be moved off track by 15%. If the mark is still unreadable, the head can be moved off track by 20%. In this sequential manner, if the synchronization mark is unreadable due to debris, asperities, skewed positioning relative to the head, translated positioning relative to the head, or the like, the movement of the head away from the traditional recording path may yield readable mark information. Other techniques can utilize the remapping of data where possible, so that once recovered, data can be moved to a readable position. Still other techniques involve moving the head by seeking to a different adjacent track and then returning to the previously unreadable mark. The physical movement of the head itself can, for example, dislodge obstructive debris allowing the track to be read.
Sometimes, however, the synchronization mark becomes unreadable after format time, and these conventional data recovery techniques may be ineffective. In these circumstances, there is a problem that the synchronization of data may not be possible due to the unreadability of the synchronization mark. If the synchronization mark is not readable, the retrieval of subsequent data sectors becomes a difficult task.
The present invention relates to a data recovery technique for recovering unrecoverable data from a sector having a synchronization mark damaged after formatting time or a synchronization mark that has been written improperly. The present invention recognizes that conventional or traditional data recovery techniques may be applied first, but if these techniques are ineffective, these techniques can be bypassed in favor of a separate recovery mode. In this separate mode, based upon overall design parameters of a disk drive system and the recording medium format, a synchronization mark starting position is estimated. The accuracy of that position is determined ex post facto, for instance, by ECC analysis. If the estimated starting position does not result in the recovery of data, iterative estimates are made within a window relative to the estimated starting position. These subsequent positions are analyzed for accuracy as well. Once an estimate matches the actual starting position of the synchronization mark, the data in the sector can be recovered.